This invention relates to a detectable card containing a plurality of LC tuning circuits and an entry and departure checking apparatus utilizing the same, and more particularly to a detectable card containing a plurality of LC tuning circuits the presence of which can be detected when at least one of said LC circuits is caused to sense the previously designated resonance frequency of an electric wave, and to an entry and departure checking apparatus utilizing the same.
A prior art card comprises a simple LC tuning circuit made up of an inductance L, a capacitance C and a resistor R, as shown in FIG. 1, and these impedance elements are sandwiched between simple covers.
When a customary detectable card having such construction is caused to sense the resonance frequency of an electric wave emitted from an electric wave transmitting and receiving apparatus, not shown, installed at an exit of a shop, the electric wave transmitting and receiving apparatus may produce an interference noise eventually to send an alarm signal or to detect the state of an absorbed electric wave energy to produce an electric signal. For this reason an article containing a detectable card provided with such an LC tuning circuit can be detected at the exit of a shop. However, since the prior art detectable card utilizes an ordinary coil and capacitor, the electric circuits are liable to be damaged, thus requiring a large number of manufacturing processes in case of its mass production, which entails large production costs as much. Moreover, as the finished card has a thickness of some extent, it is rather inconvenient to handle and carry with.
An entry control system, meanwhile, has been used in which a person who carries a plastic card having a size of a credit card provided with a magnetic strip can open a door or gate automatically by using the card. More particularly, when a card with a preset code is inserted into pass terminals installed on the inside and outside of a door, the door is caused to open and then automatically closed in accordance with a predetermined mode after a person carrying the card has passed through the door. This system, however, is not convenient because each time a door is to be opened, the person must take out the card and insert it into the pass terminals each time.
In the case of an optical identification card system, it is also necessary to pass the card through a checking device, that is, the card carrier must mount the card on a suitable portion of the body not to intercept a light beam utilized to detect a specific code on the surface of the card. This not only makes troublesome the use of the card but also can be viewed by third persons.